Sleep is a vital life process that occurs in virtually every organism sufficiently examined. Inadequate sleep regulation has become a prevalent health issue that potentially contributes to a variety of physiological and mental health disorders. However, very little is known about the neural, genetic, and molecular underpinnings of sleep regulation. Two fundamental processes are thought to regulate sleep, a circadian component (Process C) that governs sleep timing and a homeostatic component (Process S) that drives sleep as a function of prior wakefulness. Studies performed in both the fruit fly, Drosophila melanogaster, and mice have revealed evolutionarily conserved transcriptional feedback loops at the core of circadian clocks driving Process C. A key circadian transcriptional activator Clock (Clk) also regulates sleep amount and maintenance in both flies and mice, genetically linking Processes C and S in diverse organisms. The ultimate objective of this proposal is to determine the function of the circadian network in sleep regulation. In the first specific aim, we will assess the function of circadian pacemaker neurons in sleep duration and consolidation by testing flies lacking certain subsets of the pacemaker circuit. In the second, we will determine the role of the circadian transcriptional feedback system in the regulation of sleep by examining sleep behavior in a series of circadian mutants and through rescue of CLK-target expression. In the third, we propose to uncover novel molecular mechanisms by which the circadian system imposes its influence on sleep regulation. Using a candidate gene approach, we will study the function of CLK-activated, circadian-regulated, and sleep-regulated genes using an array of genetic reagents available in flies, including the newly available RNAi library. [unreadable] Relevance: Defects in sleep regulation have become an emerging threat to public health, performance, and safety. While experiments outlined in this proposal are designed to improve our understanding of the neural, genetic, and molecular basis of the sleep-wake cycle, we expect the findings will help foster strategies to offset the rising health issues caused by inadequate sleep. [unreadable] [unreadable]